The present invention relates generally to estimating a load and more particularly to a method for load estimation using only DC link voltage measurements to determine an average load current which is used as an initial condition for optimally controlling a converter connected between a backup DC energy source and a customer load.
Known inverter systems (i.e., commercially available motor drives and uninterruptable power supply (UPS) systems, etc.) experience problems due to utility power outages and sags in power. Normally, the DC link of the inverter system is supported by the utility via a rectifier. When the utility fails, the DC link voltage falls as the inverter continues to draw from it. The voltage quickly falls to a level insufficient to support the inverter, and the system subsequently trips off line.
In certain situations, a backup energy source delivers supplemental energy to stop the fall of the DC link and hold it at a potential above the trip point. Energy is provided through a power converter which is typically waiting in a standby mode until the DC link falls. This converter must assume the entire load as quickly as possible so as to prevent the further collapse of the DC link voltage.
Most applications of such a backup energy source do not provide for or allow the use of any in-line instrumentation to measure the load current. Typical ways of measuring the load current to determine the load include inserting a meter in series to measure the load current. However, often times the situation is such that the customer load is inaccessible or it is undesirable to open a line and insert such a measurement device. A system for estimating a load to optimize a power switchover is therefore needed which augments and supplements the customer's system without invasively violating it.